120 RESPIRATION 



the air have led to various results at the hands of different observers. 

 Regnault and Reiset did not discover any increase in the consumption 

 of oxygen when this gas was largely in excess in the atmosphere. 



The results of confining an animal in an atmosphere composed of 

 twenty-one parts of oxygen and seventy-nine parts of hydrogen are re- 

 markable. When hydrogen is substituted for nitrogen, the consumption 

 of oxygen is largely increased. This has been attributed to the greater 

 refrigerating power of the hydrogen ; but a more rational explanation is 

 in its greater diffusibility. Hydrogen is the most diffusible of gases ; 

 and when introduced into the lungs in place of nitrogen, the vitiated 

 air, charged with carbon dioxide, is undoubtedly more readily removed 

 from the deep portions of the lungs, giving place to the mixture of 

 hydrogen and oxygen. It is probably for this reason that the quantity 

 of oxygen consumed is increased. It is probable that the nitrogen of 

 the air plays an important part in the phenomena of respiration, by 

 virtue of its degree of diffusibility. 



In view of the great variations in the consumption of oxygen, de- 

 pendent on different physiological conditions, such as digestion, exercise, 

 temperature etc., it is impossible to fix on any number that will represent, 

 even approximately, the average quantity consumed per hour. The esti- 

 mate arrived at by Longet, from a comparison of the results obtained 

 by different reliable observers, is perhaps as near the truth as is possible. 

 This estimate puts the hourly consumption at 1220 to 1525 cubic inches 

 (20 to 25 liters), " in an adult male, during repose and under normal con- 

 ditions of health and temperature." 



In passing through the lungs, the air, in addition to losing a certain 

 proportion of its oxygen, undergoes the following changes : 



1. Elevation in temperature. 



2. Gain of carbon dioxide. 



3. Gain of watery vapor. 



4. Gain of ammonia. 



5. Gain of a small quantity of organic matter. 



6. Gain, and occasionally loss, of nitrogen. 



The elevation in temperature of the air that has passed through the 

 lungs has been studied by Grehant. He found that with an external 

 temperature of 72 Fahr. (22.22 C.), respiring seventeen times per min- 

 ute, the air taken in by the nares and expired by the mouth through an 

 apparatus containing a thermometer carefully protected from external 

 influences, marked a temperature of 95.4 Fahr. (35.22 C.). Taking in 

 the air by the mouth, the temperature of the expired air was 93 Fahr. 

 (33.89 C.). At the beginning of the expiration, Grehant noted a tem- 

 perature of 94 Fahr. (34.44 C.). After a prolonged expiration, the tern- 



